Water quality and wetlands: defining ecological categories and links with land-use

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South Africa has excellent long-term, water quality monitoring data for rivers, but this is not the case for wetlands. Wetlands are naturally more variable in terms of water chemistry than rivers, both spatially and temporally. One of the consequences of the lack of data coupled with variable water quality, is that there is a poor understanding of the range of water quality parameters that occur in wetlands, both under natural conditions and in their impacted state, and how this varies between different types of wetland. This projects contributes to an understanding of the water quality conditions in wetlands, how this changes with wetland type, level of inundation, or
land-use in the surrounding catchment.
The overall aim of this project was to further the understanding of the relationships between water quality in wetlands, catchment environmental condition, land-use and biotic response. Following extensive literature review and data collection, the data was re-analysed. The possible existence of regional patterns of water quality conditions in wetlands was examined. One of the results of this work is a better understanding of what represents the Reference water quality condition for different wetland types and whether this concept can legitimately be applied to wetlands.
Boundary values were derived to delineate levels of water quality impact for wetlands in three Ecological Categories, though data constraints meant that these are best guesses. Detailed, site specific boundary determinations are still required. However the method is now available and consistency can be achieved. A simply spread sheet to link land use with water quality was developed and tested on six wetlands with reasonable data. A tool has been produced for broader use in the wetlands reserve determinations.
However, more data are needed to ground truth the methods developed.
The results from this study have shown that there is natural variation in water quality between different wetland types. Specifically depressions have naturally higher levels of constituents than other wetland types. The results from this study have also shown that water quality varies naturally by region and that pH, and possibly nitrates plus nitrites, are lower in Fynbos wetlands. These findings, however, were not taken into account during derivation of this set of guidelines. With additional data, the boundary values need to be revisited and different values derived for depressions. More work is also required to develop and validate the diatom assessment index for wetlands.